Magnesium-substituted zinc-calcium hydroxyfluorapatite bioceramics for bone tissue engineering

Abstract

Hydroxyfluorapatite (HFAp) materials possess a structural and compositional similarity to bone tissue and dentin. These bioceramics facilitate various physiological functions, including ion exchange within surface layers. Additionally, magnesium (Mg) serves as a primary substitute for calcium in the biological apatite found in the calcified tissues of mammals, while zinc (Zn) contributes to overall bone quality and exhibits antibacterial properties. Although multiple studies have examined the individual substitution of ions within the hydroxyapatite (HAp) structure, no research to date has investigated the simultaneous substitution of zinc, fluoride, and varying amounts of magnesium in calcium HAp. This study explores the incorporation of magnesium into the structure of zinc-calcium hydroxylfluorapatite. A series of ion-substituted apatites, represented as Ca_9.9-xZn_0.1Mgx (PO₄)₆(OH)F with 0 ≤ x ≤ 1, were synthesized. Characterization of the produced samples confirmed that they were monophase apatite, crystallizing in the hexagonal P63/m space group, with only a slight impact on crystallinity due to magnesium doping. Pressure-less sintering of the samples demonstrated that maximum densification, approximately 94%, was achieved at 1200 °C with a sintering dwell of 1 h for the sample with x = 0.1. Furthermore, the Young's and Vickers hardness of this sample reached peak values of 105 and 5.02 GPa, respectively. When immersed in simulated body fluid, the formation of an amorphous CaP which can subsequently be crystallized into crystalline phase on the surface of dense specimens was observed, indicating the ability to bond with bone in a living organism and their potential use as substitutes for failed bone and dentin filling and coating.